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Christie's is selling a German three-rotor Enigma cipher machine, from around 1939, as part of its natural history sale next month. The code machine, estimated to be worth £40,000-£60,000 was widely used during World War II to encrypt and decode messages sent between the military and its commanders.

Its interchangeable rotors made a total of 15 billion billion possible readings for each character. This was considered too complex to be broken, but due to the efforts of Alan Turing and a team of analysts at Bletchley Park, the mechanism was cracked, enabling the allies to read all secure messages